Tensioned Metastable Fluid Detector (TMFD)

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
Dan Knapp
Posts: 189
Joined: Wed Aug 06, 2008 12:34 pm
Real name: Dan Knapp

Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Dan Knapp » Tue Oct 24, 2017 12:05 pm

That indeed is how the acoustic TMFD works as well as the bubble detector tubes.

Dan Knapp
Posts: 189
Joined: Wed Aug 06, 2008 12:34 pm
Real name: Dan Knapp

Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Dan Knapp » Wed Oct 25, 2017 7:02 pm

ATMFD diagram.pdf
(116.28 KiB) Downloaded 36 times
I've done some further study on the Acoustic Tensioned Metastable Fluid detector, and it looks like it might be a more useful one for the amateur to try to home brew than the centrifugal variety. There are a couple of papers on it in Nuclear Instruments and Methods in Physics Research A (Vol 673, p.89, 2012; Vol 784, p. 176, 2015) for those who can access this journal. A diagram of the detector is attached (from the vol. 673 paper). It uses a 70 mm OD x 150 mm long, 3 mm wall, quartz tube as the basic structure. The reflectors are hollow quartz discs. The PZT driver is a ring shaped transducer polarized in the radial direction and operated at about 20 kHz. Conceivably, one could cobble together something from a cheap ultrasonic cleaner. The challenge would be to devise a reflector to get a resonant standing wave in the liquid. This particular design was to enable placing four event detectors around the outside for directional sensing; a detector for fusor work could be simpler with a single transducer. Since the tensioning is switching on and off at 20 kHz, the cavitation events do not grow to be dramatically visible as in the CTFMD, and thus need to be detected electronically using a PZT detector (perhaps an element from a PZT buzzer?). The detection circuit uses a high pass filter to exclude the acoustic drive frequency. You cannot set the neutron energy threshold with the ATMFD, but it has the advantage of much less dead time than the CTMFD.
The ATMFD looks like something within the realm of the home brew builder. Even if one had to buy the transducers, they are not outrageously expensive, and the driver electronics could be pretty simple (the published version used about 4.5 watts of 18.3 kHz power). Oscillator and amplifier kit modules (e.g. Velleman kits) should work. If there is someone among the readers knowledgeable in ultrasonic acoustic design, they might have a suggestion for a simpler resonant cavity that could be used.

Silviu Tamasdan
Posts: 147
Joined: Wed Jun 28, 2006 11:17 pm
Real name: Silviu Tamasdan
Location: Connecticut

Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Silviu Tamasdan » Thu Oct 26, 2017 9:54 am

I suspect that the design of a resonant cavity will be strongly depemdent on the working fluid chosen, in particular of the speed of sound in said fluid.
There _is_ madness to my method.

Dan Knapp
Posts: 189
Joined: Wed Aug 06, 2008 12:34 pm
Real name: Dan Knapp

Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Dan Knapp » Thu Oct 26, 2017 12:39 pm

The speed of sound in the fluid will definitely affect the reflector spacing. I failed to mention that they used acetone as the fluid in the ATMFD.

User avatar
Finn Hammer
Posts: 84
Joined: Sat Mar 05, 2016 12:21 pm
Real name: Finn Hammer
Contact:

Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Finn Hammer » Wed Nov 01, 2017 9:09 am

Dan Knapp wrote:
Sun Oct 22, 2017 8:59 pm

The TMFD shown at the meeting is being used by Kai Masuda’s group at Kyoto University in a detection system for “special nuclear materials” being developed for the Tokyo Olympic Games. They are using a portable fusor with a 17 cm diameter water cooled chamber operated at 120 kV to generate 5 X 10e7 neutrons per second to actively interrogate suspicious objects.
Dan,

"a 17 cm diameter water cooled chamber operated at 120 kV to generate 5 X 10e7 neutrons per second"

I cannot seem to get my mind off these numbers, and have to ask: What is in the center of that 170mm diametre fusor.

What does a grid supporting this power level look like?

And do you have any data describing the current and pressure in that fusor.

Cheers, Finn Hammer

Dan Knapp
Posts: 189
Joined: Wed Aug 06, 2008 12:34 pm
Real name: Dan Knapp

Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Dan Knapp » Wed Nov 01, 2017 6:11 pm

In previous reports, they used a spherical grid cathode made from molybdenum sheet material rather than wire, so I assume that is what they are using now. I don't have any specific information on the current and pressure they are using. They have been working on compact neutron sources for several years, and Masuda has made other meeting presentations on this work; so a Google search might yield more details.

Dan Knapp
Posts: 189
Joined: Wed Aug 06, 2008 12:34 pm
Real name: Dan Knapp

Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Dan Knapp » Wed Nov 01, 2017 8:16 pm

The following paper is available online:
http://www.taka.qst.go.jp/tokai_center/ ... Ohgaki.pdf
It shows a diagram and a picture of the cathode of an IEC neutron source that gave 1.2 x 10e8 n/sec operating at 190 kV and 36 mA in pulsed mode (likely key to avoid melting the whole thing at these power levels). The operating pressure is not stated.

Silviu Tamasdan
Posts: 147
Joined: Wed Jun 28, 2006 11:17 pm
Real name: Silviu Tamasdan
Location: Connecticut

Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Silviu Tamasdan » Wed Nov 01, 2017 9:51 pm

That seems to be a different device though. The chamber diameter is about 3 times bigger (56cm vs the stated 17cm). Even the grid is 20cm diameter.
There _is_ madness to my method.

User avatar
Finn Hammer
Posts: 84
Joined: Sat Mar 05, 2016 12:21 pm
Real name: Finn Hammer
Contact:

Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Finn Hammer » Thu Nov 02, 2017 3:14 pm

Dan Knapp wrote:
Wed Nov 01, 2017 8:16 pm
The following paper is available online:
http://www.taka.qst.go.jp/tokai_center/ ... Ohgaki.pdf
Dan,

Thank you, for taking the time to dig out this PDF. I appreciate it.

Cheers, Finn Hammer

Post Reply